1. Field of the Invention
The invention concerns a plastic closure cap according to the preamble to claim 1. These types of closure caps are mainly used for the closure of containers, and in particular of bottles with liquid contents.
2. Description of Related Art
If the closure cap is used on containers with beverages containing carbon dioxide, the closure cap must under certain conditions also remain reliably in contact with the container mouth under considerable gas pressure. For this reason, retaining means are anticipated on the countainer mouth and on the inner side of the closure cap by which means the closure cap can engage with the container mouth. As a result, however, intentional manual removal of the closure cap will also be hindered. In order to solve this problem, various suggestions are known.
For example, CH-PS-529 022 shows a plastic closure cap provided with a strap engaging around the outer wall, by which means the closure cap can be withdrawn from the container mouth under the exertion of force.
CH-PS-553 696 shows a closure cap which, on its casing, is provided with a press lug and frangible points. The closure cap can be removed by means of depressing the press lug. Through the extertion of pressure on the press lug, the frangible points will sever, permitting the retention element to be overcome more easily. Apart from that, severed frangible points will reveal unauthorized opening of the container.
DE-DO-1 782 059 shows a plastic closure cap which is provided with a pull-off ring and integrated zones of weakness on the cap casing. If, in order to open the closure, a force is applied to the pull-off ring, the said zones of weakness will break, by which means opening of the closure cap will be facilitated. The closure cap retaining elements possess additional sections of less thickness and if necessary also perforations, in order to impart increased flexibility to the cap.
However, all these closure caps suffer various disadvantages: either considerable force will still be required in order to open the cap, or the closure is so elastic that it can easily be ejected from the container mouth by the internal pressure. On the one hand, with solutions that recommend press elements or press lugs, the disadvantage is that only a relatively short lever arm can be created; on the other hand, the zones of weakness on the lower skirt edge are restricted, so that breaking of these zones of weakness will not facilitate opening to any degree.
The object of the invention is thus to avoid the disadvantages of the state of the art, and therefore in particular to create a plastic closure cap for beverages containing C0.sub.2 which can be removed from the container mouth with the least possible application of force. In addition, the closure cap shall also display initial opening of the container.